The present invention is directed to an optical imaging system for fabric seam detection in which there is no contact between the sensor and the web of material being monitored.
During the course of manufacturing various webs of material, for example, textiles, such materials are typically processed in the form of long strips. Since it is often time consuming and costly to start up equipment and machinery for processing such long webs of material, such machinery frequently operates continuously for long periods of time during which it is desirable that the web being processed be formed into one continuous element. However, such a continuous web of material is invariably fabricated by piecing together shorter lengths of such web material. For example, in textile manufacturing, the continuous web of fabric processed by the textile machinery is formed by sewing together shorter lengths of fabric.
The result of such a procedure for forming a single continuous web of material is that seams or other periodic patterns are introduced into the web at periodic but unpredictable intervals. The detection of the seams or other periodic patterns is of great concern to the web manufacturers, since such seams or discontinuities are generally somewhat thicker than the web of material being processed and can frequently damage the processing machinery.
An example of the prior art approach to the detection of seams or other protrusions on a running web is shown in U.S. Pat. No. 3,748,414, issued on Jul. 24, 1973, to Holm. The device disclosed in that patent utilizes a sensor which bears against the web surface. A pair of spaced parallel rollers mounted on a common pivoted bracket engage opposite sides of the web. One roller is positioned opposite the sensor and the other roller is positioned opposite a fixed position roller. A mechanism is provided for urging the pivoted rollers against the web surfaces such that a change in web thickness will automatically calibrate the sensor to the roller gap by self-adjustment of the pivoted rollers.
The system of Holm has the disadvantage that it is a contacting type of web measurement system with the attendant drawbacks that such a contacting system is mechanical in nature and thus prone to frequent adjustment and/or malfunction and that such mechanical systems can have the effect of damaging or discoloring the web they are used to monitor.
U.S. Pat. No. 2,091,522, issued on Aug. 31, 1937, to Perry, shows a seam or defect detector for sheet material for use in connection with a measuring table over which the sheet material is drawn and utilizes a mechanical system which contacts the web and indicates when a seam or defect has been detected. The seam detector of Perry, however, suffers from the same drawbacks as that of Holm, because it is a mechanical contact type system and therefore requires frequent adjustment. It also uses operating parts which may become worn or inoperative.
A non-contacting approach for detecting splices in the web of a printing press is shown in U.S. Pat. No. 4,901,577, issued Feb. 20, 1990, to Roberts. In that patent, the web in a high speed printing press passes between a transmitter and receiver. The transmitter produces ultrasonic sound which is received by the receiver after attenuation by the web. The received ultrasonic sound is converted into an oscillating electrical signal of corresponding frequency which, after being amplified and filtered, is impressed upon a peak detector and comparator is long as no splices are found in the web, the reference potential remains undisturbed. In the event a splice is detected, a periodic pattern is created by the comparator in its oscillating signal. That periodic pattern is detected and is utilized to trigger a marking device for imparting a suitable mark to the web both before and after the splice.
A method and apparatus for analyzing the formation of a web of material by generating a formation index utilizing a linear array CCD camera is shown in U.S. Pat. No. 4,857,747, issued Aug. 15, 1989, to Bolton et al. In that patent, a light source is located beneath and perpendicular to the direction of movement of a web of material and the web passes between the light source and the CCD camera. The camera generates signals corresponding to the light intensity across the entire width of the web as compared to a single point for sample measurements. The signals are then processed to generate a full width formation profile of the web in real time. Utilizing a pulse generator which is coupled to a roller which engages the web, the scanning rate of the camera is regulated such that it corresponds to the speed of the web.
The Bolton et al. system is directed to a web formation system, and not a web inspection system, as is the present invention. In the Bolton et al. system, all light intensity variations are measured for a given area and not just the areas that exceed preset threshold limits.
Thus, in the Bolton et al. system, the light intensities across the entire web are converted into analog electrical signals which are in turn converted into digital signals.
The Bolton et al. system is not directed to a web inspection system and can only be used in instances where the web allows light to pass through it. Thus, for many applications in which the web is not transparent, the Bolton et al. system is not operative. Furthermore, the Bolton et al. system is complex and utilizes a large amount of electronic equipment for operation.